In my article on whether low carb diets are better than other diets I explore the contesting stances on this subject in terms of both weight loss and safety. Much of the information out there is light on facts, or very biased in terms of which research studies they present. In this article on which diets are most effective I wish to present what I see as a representative cross section (rather than exhaustive list) of some of the more important scientific research on which diets are most effective.

Particularly, we will compare the research on low carbohydrate, high fat diet to several others including specifically the low fat, low calorie type diet.

I have tried to summarise the a fair number of research finding, so this is another article for your research hat and large mug of coffee!

Diet sustainability

As a psychologist I am always interested in our actual happiness! I think we have all observed people where the diet itself made someone we know way more unhappy (or certainly not less so) than they were with the extra weight. Generally speaking this can be due to the restriction in calories, but also often to our bodies reaction to the composition of our calories from the diet. Particularly where one of the goals of the diet is lifestyle change, this can be key!

So I delved around to find a study that sheds light on this issue, and luckily Brinkworth et al., (2009) had the same idea. They compared a very low carbohydrate diet with a low fat diet in overweight and obese subjects over a 1-year period. Although both diets improved scores on both depression and anxiety scales ‘there was a favorable effect of an energy-restricted LF [low-fat] diet compared with an isocaloric LC [low-carbohydrate] diet on mood state and affect in overweight and obese individuals’. Most research appears to bear this out.

I did manage to find one study that found the opposite result though. Yancy et al., (2004) compared low-fat and low-carb diets in 120 overweight, high lipid-count subjects. They found that the low-carbohydrate diet had better client retention as well as greater weight loss.

Research studies showing low carb diets to be most effective in weight loss

Samaha et al., (2003) compared the efficacy of low-carb and low-fat diets on a sample of 132 obese subjects. Between-group and overall differences were small but significant, and the authors called for cautious interpretation. Nevertheless, they did conclude that ‘Severely obese subjects with a high prevalence of diabetes or the metabolic syndrome lost more weight during six months on a carbohydrate-restricted diet than on a calorie- and fat-restricted diet, with a relative improvement in insulin sensitivity and triglyceride level’.

Greene et al., (2004) compared a low-fat diet, low-carb diet, and low carb diet with an additional 300 calories over a 12 week period. The low carb group lost the most weight, averaging 23 pounds, followed by the low-carbohydrate diet with the additional 300 calories (20 pounds) and then the low-fat diet (17 pounds).

Gardner et al., (2007) compared four different diets (Atkins diet, LEARN diet, Zone diet, Ornish Diet). They studied a sample of 311 premenopausal obese and overweight women over a 12-month period. Results showed that the women on the Atkins diet lost more weight than the women on the Ornish, Zone and LEARN diets, and concluded that a ‘low carbohydrate, high-protein, high-fat diet may be considered a feasible alternative recommendation for weight loss.’ However they also cautioned that questions remain about the long term feasibility of remaining on low-carbohydrate high-fat diets.

Meta-analyses demonstrating low carb diets to be more effective in weight loss

Hession et al., (2007) also conducted a meta-analysis of low-carb versus low-fat diets, between 2000 and 2006. They used similar admission criteria to Nordman et. al., 2006, (mentioned below) and obtained 13 studies that they felt met admission criterion. Interestingly enough (and relevant to their conclusions) their methodological criteria appear to have been somewhat less strict than Nordman et al., as they included a lot more studies than Norman et al. for the overlapping time period. The authors found that over a 6 month period low-carbohydrate diets achieved greater reduction in weight. It is particularly interesting to note that the results and conclusions of the Hession meta-analytic study are significantly different to those of the Nordman meta-analytic study, despite a large overlap in both time period and studies used.

Meta-analyses demonstrating low carb diets to be (no more or) less effective in weight loss

Nordman et al., (2006) conducted a meta-analysis of all studies comparing low-carb diets without calorie restriction with a low fat diet in individuals with a BMI of at least 25 (i.e. overweight or obese). Analyzing the five studies that met the inclusion criteria they reached the conclusion that "low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year’. The authors expressed ‘caution against the conclusion that low-carbohydrate diets can be generally recommended to promote weight loss’. They noted that trials of reduced-fat diets, in conjunction with other lifestyle modifications such as increased physical activity, have demonstrated long-term maintenance of weight reduction and delayed onset of diabetes.

Bravata et al., (2003) conducted a meta-analysis of weight loss research. They concluded that weight loss was related to calorie intake, and beyond this variance eating fewer carbs was not significantly associated with weight loss.

Astrup et al., (2004) conducted a review of literature on low-carb diets and concluded that the weight loss achieved was not in fact associated with the restriction of carbohydrates, but rather correlated with the reduction in calories and indeed the length of the diet. They felt their conclusions were not particularly supportive of low-carbohydrate diets, but nevertheless recommended longer term studies to examine their effectiveness and safety.

Research studies showing low carb diets to be no more effective than low fat diets

Bowman et al., (2002) conducted a survey of 10 014 American adults (who were not necessarily dieting at all) and correlated their carbohydrate intake percentage with their BMI (body mass index). He actually found that people on a high carbohydrate diet were more likely to be of a healthy weight (BMI<25) which cast doubt on the efficacy of low carb diets.

Foster et al., (2003) randomly assigned 63 obese subjects to either a high-carb or high fat group. The low-carb group lost a significantly greater amount of weight over the first 6 months (around 4% more than the low-fat group), but there was no significant difference between the groups over a full year.

Stern et al., (2004) compared a low-carb diet with a conventional diet using a sample of 132 obese subjects over a 1 year period. Results showed that there were no significant differences in weight loss between the two groups.

Two studies supporting the Mediterranean diet as more effective long term than the low carb diet

Shai et al., (2008) conducted a 2-year longitudinal study on 322 moderately obese subjects. They compared a low-fat calorie-restrictive diet (based on American Heart Association recommendations in 2000), a Mediterranean calorie-restricted diet, and the Atkins diet (but where the subjects were encouraged to choose vegetable sources of fat and protein to avoid trans fats). In my opinion this version of the Atkins diet is unlikely to be the one followed by most of its supporters at the moment, but is almost definitely healthier than the standard one for the cardiovascular system. Over the first 2 years drop-out rate was only a shade over 15%. The quasi-vegetarian Atkins diet had the greatest weight loss over this period. However, a follow-up study 4 years later showed that the subjects had regained 2.7kg, 1.4kg and 4.1kg respectively on the low-fat diet, Mediterranean diet and ‘Atkins’ diet, leaving an actual weight loss over the 6 years of 0.6kg, 3.1kg and 1.7kg. Clearly those who began on the Mediterranean diet maintained it the best over time, and had the greatest overall weight loss.

Ajala et al., (2013) conducted a meta-analysis of the literature comparing low-carbohydrate, vegetarian, vegan, low–glycemic index (GI), high-fiber, Mediterranean, and high-protein diets with control diets including low-fat, high-GI and low-protein diets, in the management of diabetes. Low-carbohydrate and Mediterranean diets led to significantly greater weight loss, again with the Mediterranean diet being significantly superior in this regard.

An interesting study concluding in favour of a low GI diet

Ebbeling et al., (2012) compared the Atkins diet, a low-fat high-carb diet and a low glycemic index diet in order to compare resting energy expenditure, total energy expenditure, as well as various other hormonal and metabolic markers. They studied 21 overweight and obese subjects over a 4-year period. The low-fat diet produced reductions in energy expenditure and serum leptin they felt would result in weight regain, and unfavourable effects on most of the metabolic syndrome components. The (very) low-carbohydrate diet had the most beneficial effects on energy expenditure and several metabolic syndrome components. The low–glycemic index diet appears to have qualitatively similar, although smaller, metabolic benefits to the very low-carbohydrate diet, but without the harmful effects on physiological stress and chronic inflammation.

They concluded that a diet that focused on reducing glycaemic load (as opposed to radically reducing carbohydrates or dietary fat) would probably work best for weight-loss maintenance and cardiovascular disease prevention.

Conclusions

You might want to consider reading my article exploring whether low carb diets are better than other diets before drawing your own conclusions. In my opinion though there are no clear winners in terms of weight loss efficacy. Different diets appear to have different strengths and weaknesses, with low carb diets perhaps favouring short-term effectiveness rather than long-term effectiveness.

In fact in many ways in the low carb versus low fat war, the Mediterranean diet and low GI diet came up trumps, although much more research on them both is needed. However, they do appear as or more effective over the medium to long term, easier to sustain, and quite possibly safer.